As known, an x-ray imaging system at least comprises an x-ray tube assembly configured to generate and emit an x-ray and a detector configured to detect the x-ray that passes through a region of a subject, such as a human body, to be examined. The detector generates an electrical signal based on the detected X-ray and transfers the electrical signal to a processing unit to form an image of the region to be examined. When the region to be examined is imaged, a patient may need to maintain a standing posture. For another patient, it may be necessary to lie on his back when the region to be examined is imaged. Thus, the x-ray tube assembly should be capable of being rotated between a first position in which the x-ray is projected for example substantially vertically onto the region to be examined and a second position which is spaced from the first position by 90° about the rotating axis of the x-ray tube assembly and in which the x-ray is projected for example substantially horizontally onto the region to be examined.
FIG. 1 shows a partial view of an x-ray tube assembly of a conventional x-ray imaging system. As shown in FIG. 1, the x-ray tube assembly 1 comprises an x-ray tube 3 configured to generate and emit an x-ray and a collimator 5 configured to collimate the x-ray generated by the x-ray tube 3 onto a region of a subject such as a human body to be examined. The x-ray tube assembly 1 is rotatably attached to a supporting part 7 through a tube arm 9 and a latching mechanism 11. The supporting part 7 is vertically movably mounted onto a tube column 13. FIG. 2 is a schematic view showing a latching mechanism in which a rotary plate is locked in the first position, FIG. 2A shows an orientation of an x-ray tube assembly corresponding to FIG. 2, FIG. 3 is a schematic view showing a latching mechanism in which a rotary plate is locked in the second position which is spaced from the first position by 90° about the rotating axis of the tube assembly 1, and FIG. 3A shows an orientation of an x-ray tube assembly corresponding to FIG. 3. As shown in FIGS. 2 and 3, the latching mechanism 11 comprises a rotary plate 15 to which the tube arm 9 is fixed and a spring-loaded latch 17. The rotary plate 15 is circular in shape and comprises a first notch 15a, a second notch 15b and a third notch 15c disposed on the periphery of the rotary plate 15. The second notch 15b and the third notch 15c are spaced from the first notch 15a by 90° and from each other by 180° about the rotating axis of the tube assembly 1. The spring-loaded latch 17 may be pressed removably into the first notch 15a to lock the x-ray tube assembly 1 in the first position in which the x-ray is projected substantially vertically onto the region to be examined. By grasping a handle 19 on the x-ray tube assembly 1 and rotating the x-ray tube assembly 1 to disengage the spring-loaded latch 17 from the first notch 15a against a force applied to the spring-loaded latch 17 by a spring, the rotary plate 15 is rotated so that the spring-loaded latch 17 may be pressed removably into one of the second notch 15b and the third notch 15c to lock the x-ray tube assembly 1 in the second position in which the x-ray is projected substantially horizontally onto the region to be examined. Of course, the spring-loaded latch 17 may lock the x-ray tube assembly 1 in a third position which is spaced from the first position by 90° and which is opposite to the second position when the rotary plate 15 is rotated in an opposite direction. Although the x-ray tube assembly 1 in the first position is aligned accurately to guarantee that the x-ray is projected substantially vertically onto the region to be examined, the x-ray is not always projected substantially horizontally onto the region to be examined when the x-ray tube assembly 1 is locked in the second position because of stack up of various tolerances such as manufacturing tolerances of tube arm, tube column, rail etc. Thus, more relevant parameters need to be carefully and repeatedly aligned, including the first position and/or the second position latching alignment during installation of the x-ray imaging system because the alignment of the first position latching and the second position latching are coupled with one another. This makes manufacturing tolerance control and installation of the x-ray imaging system much more complicated and difficult.
Thus, there is a need to make improvements on the conventional x-ray imaging system.